This project proposes a study of the radiation induced autoxidation of selected lipids and sulfur compounds of biological importance, including the chemistry, structure and motion of the resulting peroxyl radicals. Electron Spin Resonance (ESR) spectroscopy, and ab initio and semiempirical molecular orbital calculations will be employed to elucidate the relationships between structure, motion and reactivity in these systems. Our proposed project intends to focus on the following aspects of lipid and sulfur oxy radical chemistry; Elucidation, through ESR spectroscopy, of the details of the autoxidation cycle in a number of unsaturated and saturated lipids at low temperatures. In this work kinetic analyses of the rates of build up and loss of the radicals involved in lipid autoxidation as a function of temperature will be performed to find the activation energies for both oxygen mobilization, and hydrogen abstraction by lipil peroxyl radicals. Next investigation of lipid peroxyl radicals formed in lipids with increasing unsaturation will be performed to observe the effect of unsaturation on the motional averaging of the peroxyl probe. The role of sulfuroxygen radicals in autoxidation processes will be studied. Using techniques developed in our laboratory, we will determine the identify of the radical(s) formed when thiols and disulfides are irradiated in the presence of oxygen at low temperatures, and determine the importance of these radicals to the autoxidation of sulfur containing compounds. Theoretical as well as experimental characterization of the sulfur oxygen radicals will be performed. Preliminary investigations of the role of sulfuroxygen radicals in lipid oxidation will be initiated. Ab initio (Gaussian B2) and semiempirical molecular orbital calculations will be employed to develop and test models of lipid and sulfur oxy radical structure, motion, and reactivity.